• Unofficial tally indicates sharp losses for Western- backed PM Saad al-Hariri

Hezbollah and its political allies won just over half the seats in Lebanon's parliamentary elections, unofficial results showed, boosting an Iranian-backed movement fiercely opposed to Israel and underlining Tehran's growing regional clout.

Branded a terrorist group by the United States, the heavily armed Shia Hezbollah has grown in strength since joining the war in Syria in support of President Bashar al-Assad in 2012.

The gains for parties and politicians who support Hezbollah's possession of weapons risks complicating Western policy in Lebanon, which is banking on foreign aid and loans to revive its stagnant economy and receives US military support.

An Israeli minister said the outcome, which has yet to be confirmed by official results, showed the Lebanese state was indistinguishable from Hezbollah, signalling the risk of Israel hitting Lebanon's government in a future war.

The unofficial tally in the first parliamentary elections in nine years indicated sharp losses for Western-backed Prime Minister Saad al-Hariri. But he was still set to emerge as the Sunni Muslim leader with the biggest bloc in the 128-seat house, making him the frontrunner to form the next government.

Iranian media appeared to gloat at Hariri's setback. The hardline Tasnim news agency ran a report headlined: "Lebanese election result puts an end to Hariri's monopoly among Sunnis."

Lebanon's prime minister must be a Sunni in the country's sectarian power-sharing system. The new government, like the outgoing one, is expected to include all the main parties. Talks over cabinet posts are expected to take time.

“Hariri is going to be further weakened in any kind of government going forward," Andrew Tabler of the Washington Institute said. "His ability to substantially tame or restrain Hezbollah ... in Lebanon is going to be very limited."